The fluorescence-activated cell sorter will be used to quantify the number of lymphocytes and mononuclear phagocytes within several murine tumors. Utilizing specific cell surface markers for lymphocytes and macrophages, those cells will be sorted for subsequent functional analysis. The murine tumors selected for this study vary in their ability to arouse a detectable host defense and represent different histological classes. The EMT6 mammary tumor is immunogenic, the KHT fibrosarcoma is not. While these two tumors have a high macrophage content, the B16 melanoma does not. All three tumors culture well in vitro. In contrast, the Lewis lung carcinoma and 6C3HED lymphosarcoma represent tumors with low and high macrophage contents respectively but, while tumor cells survive poorly in vitro, the macrophages from them have a high plating efficiency. We plan to study the secretion of the macrophage activating factor (MAF) tumor derived lymphocytes. This factor is required for rendering macrophages tumoricidal. The clonogenic and tumoricidal activity of tumor derived macrophages and the ability of the tumor cells to elaborate macrophage growth factor (MGF) a factor necessary for macrophages to proliferate will also be determined. With this knowledge, we will be able to define in a more realistic fashion, the cellular interactions between lymphocytes, macrophages, and tumor cells within progressing and regressing tumors. Utilizing the tests, we will investigate the effect of single and fractionated tumor irradiation on the host defense elements. Mice bearing tumors will be irradiated while the tumor is in log growth and each parameter will be evaluated in animals bearing progressing and regressing tumors. Results from this study will reveal important information on why some tumors progress and others regress by defining the number of host defense cells relative to tumor cells and their tumoricidal state.